Due to the growing demand for energy throughout the world, concerns have grown about the future of the world's energy supplies. Not only are there limited supplies of oil and coal reserves available within the earth's crust, but due to the ongoing security problems and concerns that now exist throughout the world today, there has been a growing desire to reduce our nation's reliance on foreign oil.
Indeed, many energy experts believe that a successful energy solution must include the ability to harness energy from what are often called natural renewable resources, such as the sun and wind. The renewability and abundant availability of these resources make them well suited to the development of potentially viable long term solutions, and many believe that whatever efforts that are currently being made to use these resources must significantly be expanded before the world's oil and coal reserves eventually run out.
One problem associated with the use of renewable energy such as the sun and wind is that the energy is not always available when the energy is needed. Solar power, for example, is only available during the day, and is most effective when the sun is shining brightly, and therefore, the extent to which energy can be provided by the sun is not always predictable. Wind energy is also only available when the wind is blowing, and therefore, it is not a highly reliable source of energy. Another drawback to these resources is that even when energy is available, the amount of energy that they generate is not always consistent. For example, even when the wind blows, it does not always blow at the same speed, or at regular intervals, and therefore, the amount of energy that can be generated is not always consistent. The same is true of solar energy, i.e., the degree to which the sun is shining and available can be sporadic; it often depends on the weather, and therefore, it is never certain how much energy can be generated at any given moment in time.
One potential solution to these problems is to store the energy during times when the energy is available, and using the energy when it is needed most. This is often referred to as time-shifting. Nevertheless, one problem associated with time-shifting relates to the inherent inefficiencies that can result from having to store energy in one form, and then converting the energy into another form before it can be used. This is especially true of compressed air energy storage systems that store compressed air in high pressure storage tanks, wherein the energy must be converted by a generator to produce usable electricity. In such case, the energy used from storage can often end up costing more than the energy that was stored. These inefficiencies can significantly reduce the economic incentives that are needed to promote the installation of these potentially viable systems.
Notwithstanding these problems, because the wind and sun represents a significant natural resource that will never run out, there is a strong desire to develop a system that can not only harness the wind's and sun's energy, i.e., to produce electricity, but to store the energy, and do so in a manner that is efficient and cost-effective, wherein the energy that is generated can then be made available on a continuous and uninterrupted basis, so that it can be used during peak demand periods, as well as when little or no wind is available or little or no sun is available.
Moreover, there are numerous geographical scenarios, especially small island scenarios, wherein the wind blows steadily and strong all through the night when the electric power demand is small but blows weakly and variably all through the day when the electric power demand is peak. Thus there is a need to install a wind turbine farm wherein the excess energy can be collected and stored during the high wind period and then used during the weaker wind period. Energy storage is thereby required.
Moreover, while there has been a steady increase in the number of photovoltaic (PV) cell projects that have been initiated and developed in recent years, each of these projects has had a serious shortfall in electric power production particularly in the late afternoon and early evening when the power demand is high. Thus there is a need to install a PV panel system wherein the excess energy can be collected and stored during the high solar irradiation period and then used during the weaker solar irradiation period.
In island scenarios the availability of onshore real estate is limited. Thus there recently is an effort to place the compressed air pressure vessel offshore and underwater. An example of such an effort is described by Thin Red Line Aerospace. Canadian Thin Red Line Aerospace has completed the first structure specifically designed and built for undersea compressed air energy storage (CAES) in May 2011. The structure, also referred to as “Energy Bag”, was anchored to the seabed off the coast of Scotland as part of a major renewable energy research project conceived and led by Professor Seamus Garvey of the University of Nottingham and supported by European renewable energy leader E.ON. The project is the first to investigate large scale offshore storage of wind, tidal and wave power as compressed air.
Wind turbines fill the balloon-like underwater bags with compressed air that later drives electrical generators on demand. While initial application is ideally linked to floating wind turbines, excess electricity from the grid—or from clean energy sources such as tidal and wave power—can also be used to drive compressors to fill the energy bags. The technology is especially suited to countries with relatively deep waters near their coasts.
Energy bags would be anchored at a depth of approximately 600 meters (2000 feet) where the pressure of the ocean takes on the role of high performance pressure vessel. The bag is hereby relegated to a flexible, balloon like structure needing only to restrain the buoyant air bubble contained within—rather than a massive, thick-walled pressure tank of exceptional cost and complexity. At this depth the immense pressure of the ocean ensures high energy storage density, constant pressure regardless of bag volume, and pressure compatibility with existing high efficiency turbine technology. For commercial scale application, Thin Red Line has performed concept development for containment volumes to 6000 cubic meters (212,000 cubic feet).
The prototype energy bag, designed by Thin Red Line's Maxim de Jong, displaces 40 tons of seawater, and is to be anchored to the seabed by its array of Vectran® fiber tendons capable of restraining a total load of 250 tons—yet the entire systems weighs only 75 kilograms (165 pounds). The design is based on Thin Red Line's inflatable space architecture currently being investigated in several NASA programs. Thin Red Line is known for their ultra-high performance fabric structures, having notably developed and manufactured the pressure restraining hulls of the Bigelow Aerospace Genesis 1 and 2 satellites launched in 2006 and 2007, the first spacecraft on orbit successfully incorporating large volume, high-stress inflatable architecture.
The U.S. Navy (FIG. 1) is considering a similar configuration wherein the depth of water is 450 feet or 200 psig hydrostatic pressure. The advantage here is that the compressor need only operate at an efficient 200 psig rather than operating at higher pressures. Furthermore, the turboexpander/generator operation at 100 psig input pressure only requires 1-stage operation and 200 psig input pressure requires only 2-stage operation. Besides, the flexible bag material does not require special design. In this operation the flexible bag operates between completely filled to completely empty.
FIG. 4 shows the characteristics of the underground cavern CAES systems now in existence. These systems are huge and require a specific geographic location for use by a specific community, require that the walls of the cavity be located in geology with very low permeability, require multi-year planning and construction and huge investment of capital. Furthermore the underground cavern CAES requires the combustion of fuel.
The T-CAES and TL-CAES systems patented by Enis/Lieberman do not require any of the underground CAES features. It is a green system with no combustion of fuel.
The principal of the T-CAES and TL-CAES systems is herein extended to off shore locations and either under water and above the floor of the sea or lake bed or under soil beneath the floor of the sea or lake bed. This configuration is of specific interest to small island scenarios where on shore property is scarce and expensive.